Enciphering and deciphering system



`une il, l946 R E MA1-HES 2,40L877 ENCIPHERING AND DECIPHERING SYSTEMFiled 0G13. 17, 1942 2 Sheets-Sheet l jim@ my w46- R. E. MATHEsENCIPHERING AND DEGIPHERING SYSTEM 2 Sheets-Sheet 2 ATTORNEY v FiledOct. 17, l942 Patented June 11, 1946 UNITED ST Richard E. Mathes, SilverSpring, Md., assigner to Radio Corporation of America, a corporation ofDelaware Application October 17, 1942, Serial No. 462,355.

(Cl. 17g-22) 13 Claims. l

This invention relates to secret signalling systems and has particularlyto do with apparatus and a method of enciphering and decipheringtelegraph code signals so as to insure secrecy in transmission. Mysystem is adapted for use in connection with any of the well-known codesystems of telegraphy, as used for example, on radio channels and wirelines. The technique which I preferably adopt is somewhat similar tothat which is disclosed in a copending application,

kSerial No. 444,658, ii'led jointly 0n May 27, 1942,

by Loyd A. Briggs and James A. Spencer, and assigned to the assignee ofthe instant application.

As will be pointed out in more detail in the description to follow, mysystem and my method are intended to preserve secrecy with respect to anenciphering or deciphering tape by locking the same in a sealedmagazine. Such a magazine may be readily transported from place to placewithout permitting the messenger who handles the same to inspect or makecopies of the tape. Furthermore, the tape is arranged to be keptconcealed from the View of an operator who transmits and receivescryptographic messages.

In order to avoid the use of an excessively long enciphering tape Whileat the same time subjecting each baud element I the signal codecombinations to the possibility of a random polarity reversal, I havefound that such polarity reversals may be conveniently accomplished bysupplementing the perforated tape controls with random polarit7reversals to be derived from the operation of a plurality ofcam-operated switches. The cams for such switches may have codedperipheries and the number of code elements in the periphery of one campreferably differs from that of the other. The purpose of the cams, orcoding disks, in combination with the encipheri-ng tape, is to providesuch interaction that repetition of a given train of encipheringcontrols or polarity reversals will seldom occur.

Accordingly, it is an object of my invention to provide a cryptographicsystem for telegraph communications such that the signals as transmittedshall be substantially undecipherable by an unauthorized recipient.

It is another object of my invention to provide means including amagazine for completely enclosing an enciphering or a deciphering tapeand for maintaining the tape concealed from vieW at all times, evenwhile it is in operation.

It is another object of my invention to provide a combination ofenciphering tape and enciphering code. disks, the cooperation betweenwhich is such as to produce long trains of essentially random reversalsof signaling elements of a message train and, at the Same time,permitting the use of a relatively short length of enciphering tape.

Other objects and advantages of my invention will be made apparent inthe description to folloW. This description is accompanied by drawings,in which:

Fig. l shows diagrammatically a circuit diagram and apparatus to' beused' at' a transmitting station; and

Fig. 2 shows a corresponding circuit diagram and apparatus to be used ata receiving station.

Referring to Fig. 1, I show therein a telegraph transmitting unit 'Iwhich is usually termed a tape transmitting head by those skilled in theart. The transmitting head is driven at a synchronous speed by a motor 4working through a one-point clutch 8. This clutch is preferably equippedwith a magnetic control for remote operation to start the transmitterhead and the code disks at a predetermined instant. Such a magneticcontrol is shown and described in the aforementioned application ofBriggs et al.

The motor 4 is of a synchronoustype and is supplied with Valternatingcurrent from a synchronous drive amplifier 24. Control impulses formaintaining this amplifier in synchronism With a multiplex distributorare derived from a synchronous multiplex commutator 25, which will beunderstood to be mounted on the shaft of the transmitting channeldistributor. The details of the circuit connections applicable to asynchronous drive amplier are not shown since they are fully illustratedand described in my Patent No. 2,194,509, granted March 26, 1940.

The coding tape 23 issues from a delivery reel 2S and is fed oversuitable guide rollers 21 on the input and output sides of thetransmitting head. A switch 2 operated by the tape slack, in a deviceshown generally at 28, controls the closing and opening of a circuit toa motor I9, the function of which is to rotate a Wind-up reel 30. Thetape 23 issuing from the transmitter is thus fed (with occasionalpauses) to the reel 30.

The two reel-s 26 and 3&1 are suitably mounted within` a sealedcontainer or magazine 3|. This magazine has a lip'6 for egress of thetape from the loaded reel 26.

The shaft of the transmitter head i carries one of two clutch engagingmembers of the unit 8. This shaft drives a cam I I having preferably twosteps on its periphery such that a lever 32 may be moved downwardly bytension of a spring 33 twice for each revolution of the shaft. Mountedon the lever 32 is a pawl 34 which is arranged to actuate a lO-toothratchet wheel 35 for feeding the tape intermittently and at one-tenththe normal speed for usual tape transmission.

The drive shaft for the transmitter head I is sufficiently elongated tocarry two worms 36 and 31. Worm 35 meshes with a worm wheel 38 having ashaft in common with code cam 2. Worm 31 meshes with a worm wheel 39,the shaft of which also carries a code cam 3.

The peripheries of cams 2 and 3 are irregularly notched for randomcontrol of a pair of doublepole double-throw switches.v One of theswitches is operated by cam follower 40 in association with cam 2. Theother switch is similarly operated by cam follower 40a in associationwith cam 3. The gear ratio obtained by the worm 3G meshing with wormwheel 38 on the shaft of cam 2 is pref-- erably of the order of 50: 1.For cam 3 the worm 31 and worm wheel 39 have a ratio of say, 49:1.

This difference in gear ratios causes cam 2 to ro-V tate 49 times during50 revolutions of cam 3. The peripheral contours of the cams are such asto operate the switches at times determined bythe baud frequency of thecoded intelligence signals. Thus, if the raised and depressed peripheralarcs of the cams were to representmarking and spacing elements of Morsecode signals, then such elements on the circumference of cam 2 would becommensurate with 100 bauds, and on cam 3, with 98 bauds.

By connecting the output terminals of `one switch to the input terminalsof the other switch, a train of random polarity reversals is producedwhich does not repeat itself until cam 2 has made 49 revolutions.

The cam follower member 49 controls two movable contact springs a and bin a D, P. D. T. switch 8l. These movable contact springs are sandwichedbetween stationary contacts c, d, and e. Contacts c and e are bothsupplied with minus D. C. potential, while contact d is supplied withplus (-i-) D. C. potential from any suitable source. When the follower40 drops into a depression in the code cam 2, contact a makes withcontact c and contact b makes with contact d. When, however, thefollower 40 rides over a tooth of the cam 2, then contact a makeswith'contact d and contact b makes with contact e. The two positions ofthe contacts a and b, therefore, provide polarity reversals of thecircuit connections which lead to stationary contacts of a D. P. D. T.switch 82 controlled by the cam 3.

Cam 3 operates follower 49a for controlling the positions of two movablecontact springs f and g in switch 82. These contact springs aresandwiched between stationary contacts h, a', and k. Theinterconnections between the two switches 8| and 82 are such thatcontacts h and lc are connected to contact b, and contact y' isconnected to contact a.

The combination of random controls of the two switches 8| and 82 by thecams 2 and 3 results in the application of a long train of randompolarity reversals to the conductors 4| and 42. T hese conductors 4| and42 connect respectively with back contacts m and n Vof a relay 45 whosearmature-controlled contacts o and p normally engage with back contactsmand n, thus feeding the potential of conductor 4| to conductor 43 andthe potential of conductor 42 to conductor .44, The front contacts q andr are used upon energization of relay 45 when it is desired to produce aphasing impulse once per revolution of the cam 3. Mounted on the sameshaft of this cam 3 is a phasing cam 46 having one tooth 41 on itsperiphery.

In cooperation with the cam 46 is a follower 4B, the function of whichis to actuate a reversing switch 49 which is similar in construction tothe switches 8| and 82. The movable contacts in switch 49 are connectedto front contacts q and 1', respectively in the relay 45. The stationarycontacts inswitch 49 are supplied with plus (-i) and minus polarities asshown.

When relay 45 is energized by remote control, as by closing 'a switch 50at the operators control station, then the switches 8| and 82 arerendered ineffective. A single polarity reversal takes place in response'to the actuation of the follower 48 whenever it rides over the tooth 41of the cam 46.

For the sake of simplicity-in tracing the circuits for polarityreversals, I have shown the several cam-operated switches las thoughcomprising contact spring-pile-ups, where, each spring pile-up has itsmovable contacts actuated by a cam follower such as 4D and 40a. Inpractice, however, I have found it advantageous to utilize a so-calledmicroswitch which has snap-acting contact elementsV therein. The switchoperation is by means of a lever arm external to the contact housing.The lever aims correspond with cam followers 49 and 40a. Issuing fromthe switch housing are switch terminals for connection inY such circuits-as are shown and described heref inabove.

The code cams 2 and 3 are preferably settable by hand in a directionopposite to the direction of their normal rotation. VMeans (not shown)including aknob 5| and a ratchet mechanism for engagement of each codecam 2 or 3 with a hub on its shaft are provided for the purpose ofsetting the code wheels in a mutually xed phase relation, one to theother, before starting the transmitter. If desired, the knob can bearranged to engage with the ratchet mechanism only when pushed in.Furthermore, a convenient gear reduction may be provided ybetween theknob 5| and the cam shaft so as to bring the phasing to a proper settingwith precision. ThisV setting may also be facilitated by alignment of amovable index point on the periphery of each cam with respect to astationary indexpoint such as shown at the position 52.

A revolution counter I6 is driven by a star wheel riding in thecenter-hole perforations of the tape 23. This revolution counter isprovided as a guide to enable operators at each end of the circuit toset up and restart at a common spot on the tape, if for any reasonreception has been interrupted and synchronism lost. The wind-up relay30 is coupled to and operated by a separate motor |9. This motor iscontrolled by a switch 20, preferably a microswitch, in response tovariations in the tape slack. -The tape slack control unit 28 includesmovable and stationary spools 29 for guiding the tape. The amount ofslack in the tape as it issues from the transmitter determines theoperation of the microswitch 20 for closing and opening the circuit ofthe motor 9.

The message tape transmitter A message tape transmitting head rBil isdriven by a motor 6|, the power for which may bederived from asynchronous drive amplifier 62 Whose synchronism is maintained' by theaforementioned multiplex commutator 25. Within the transmiting unit El!is a keying device, or double-throw switch 63 operated by seeker pinsunder control ofi the message tapeperforat'ions. The stationary contactsof a tape-controlled polarity reversing switch 63 are connectedrespectively to plus (--l and minus terminals of the D. C. source. Thevibratory tongue lin the switch i3 is connected to one terminal on thecoil ci relay 32. The other terminal of this coil is connected to agrounded neutral point intermediate between the plus andv minusterminals of the D. C. source.

In'Y the transmitting head l a similar tape-controlled polarityreversing switch G4 is provided. Switch 6% also has stationary contactsconnected with :plus and minus terminals or the D. C. source and avibratory tongue connected through the winding of a polarized relay E5to a grounded neutral point intermediate between the plus and minuspotentials of thev D. C. source.

The tongueV of relay 32': follows the movements of the messagetape-controlled switch 53 while the tongue of relay (35 follows themovements oi' switch unit 64 under control of the enciphering tape.

Impulses or brief duration are supplied upon each revolution of thecommutator in a signal regenerator unit 1. These impulses originate at agrounded neutral potential and are fed to the tongue of relay 32 duringa fractional part of each signaling baud time unit. Whether thesignaling baud shall be characterized as a marking or a spacing elementis determined by the position of the tongue oi relay 32.

The stationary contacts of relay s2 are normally connected through amanually operable switch 57 to the outer terminals oi two coils A and Bof a keying relay @5. Positive or negative potentials are applied to theconnecting link ESS between coils A and B, in dependence upon thecoordination of polarity controls exercised by the enciphering tape andthe cams 2 and 3.

The coils A and B are so wound that a positive potential applied to linkG9 will move the relay tongue 10 to the right when it energizes coil A,and will move tongue lll to the left when coil B is energized. Anegative potential so applied reverses the movements of the tongue lil.Hence the operation of relay 56 vlull depend not only upon the currentpolarity as determined by the enciphering end of the circuit, but alsoupon the marking and spacing conditions of the message tape, since thelatter are reflected in the coil selection in relay EHS- whether coil Aor coil B.

The resultant output from relay 66 is constituted as a plus or minusimpulse, derived from the two stationary contacts of this relay. Theseimpulses are fed to the tongue I0 and thence to a so-called transmittingkicker 1I which keys the signal output circuit. The kicker 'll ismounted on a synchronous commutator of the transmitting machine andtimes the eiective portions of signals from relay 65 in accordance withthe synchronousr speed of the multiplex transmitting distributor. Relay66 is supplied with plus and minus polarities on its two stationaryVcontacts respectively.

Mode of operation In theory, the enciphering of messages by the use of'the apparatus hereinabove described is comparable with that of a systemfully described and shown in the aforementioned copending application ofBriggs et al. The marking and spacing elements of the message tape areat times transmitted as such, but when the vpolarities thereof. arereversed by the enciphering tape or by the code cams, then the signalsare rendered unintelligible because of the random effects of thesereversals. By the use of identical enciphering and deciphering tapes atthe transmitting and receiving stations respectively and by the use ofcode cams 2 and 3 started insynchronism at the transmitting andreceiving stations, the polarity reversals of the signals is made suchthat deciphering at the receiving stationis readily eiected, butotherwise the signals are substantially undecipherable;

The receiving apparatus Referring now to Fig. 2, the receiving apparatuscomprises a magazine` 31a containing the deciphering tape 23a andcooperating mechanism, the same asshown and described in Fig. 1.

Also there are shown in Fig, 2 various elements of a deciphering unitincluding a transmitting head lf2, code cams 'I3- and- 74', andcam-operated switches l5 and i6, the same as in the'enciphering systemof Fig. 1. The only difference between the arrangement at the receivingstation and that at the transmitting station lies in the provision ofcertain phasing switches and an automatic starting device at thereceiving station which are not needed at the transmitting sta-- tion.rhe starting and phasing devices for the receiving station are notherein described in detail since equivalent apparatus has beenA fullydisclosed in the aforementioned copending application of Briggs et al.-

The incoming signals are applied to a locking circuit Tl whicltimayV beof any well-known type. The output from the locking circuit is normallyconnected across the winding of polarized relay '58. This'rel'ay hasmarking and spacing contacts associated with itsV tongue, the latterbeing impulsively grounded through a synchronously driven signal shapingcommutator T9. One or the other of two winding circuits in polarizedrelay et is energized in dependence upon the position assumed by thearmature of relay 18.

The references M and S, by' which the contacts of relay 'E8 aredesignated, refer to marking and spacing conditions to be assumed bythis relay in response to incoming code signals.

Relay Sii has two windings which are respectively energizable by themarking and spacing contacts of relay i8. The interconnection betweenthe two windings is normally connected through switch lSila to thetongue of relay 83. The marking and spacing contacts of relay 83 areconnected to the output terminals of one cam-operated reversing switch15. The other cam-operated reversing switch 1'5 has its input terminalssupplied with positive and negative potentials. Conductors 84 connecteach output terminal of switch 15 with one of the input terminals ofswitch 16, respectively.

The winding of relay S3, which is a polarized relay, is in circuitbetween the tongue of the tape controlled keyer switch B5 and ground.The stationary contacts of switch 85 are connected throughV suitableresistors 36 to the positive and negative power terminals respectively.This arrangement causes the tongue of relay S3 to follow the movementsof the tape controlled keyer switch 85.

The cams 13 and 'M are manually settable to a predetermined startingphase, in the same manner as described above with respect to cams 2 and3 at the transmitter. A phasing magnet 8'! is energized bythe operationof relayv 88 upon de'- pression of a key 89, and is unlocked at aprecise moment by reception of a starting signal from the transmittingstation. Relay 88 is self-locking and is unlockedupon breaking of itsenergizing circuit through the tongue and spacing contact of relay 80.The clutch members 8a are engaged upon release of magnet 81, thusYstarting the tape unit 'l2 and the code cams 13 and 14.

VThe movablev member of switch 80 is connected to the marking contact ofrelay 8D. The tongue of relay 80 is connected through a resistor 9| tothe negative terminal of a D. C. source for operating a recorder orprinter, either of the latter being placed in service in accordance withthe setting of switch 90. Observation of the signal response of relay 8Dmay be made by plugging a synchronoscope circuit into the jack 92. 'Ihiswould be desirable when passing.

Deciphering of the cryptographic signals depends upon maintaining thedeciphering tape in step with the enciphering tape. Also the code cams'I3 and 14 must be properly phased with respect to the code wheels 2 and3. The polarity reversals due to the use of the deciphering tape and thecams 13 and 14 are combined to determine the direction of currentflowthrough one of the coils in relay 80. The sense of the receivedsignals determines which of the coils in relay 80 shall be energized,and this nally determines the throw of the armature in relay 8i)r to oneside or the other. Y

Recapitulation The method of coding is to reverse the senseviz, mark forspace or space for mark-of the message signals. 'I'his reversal occursat irregular intervals as called for by the coding key, but in no eventVcan the message continue for more than, say ten dot lengths without theoccurrence of a reversal.

The coding is accomplished by preparing paper tape of the type standardin the telegraph art. Decoding is done with an identical tape. The tapeis to run through a standardV telegraph tape transmitter. Theenciphering signals and message signals produce a coordinated effect ina polar relay such as to reverse the message signals when the codingtransmitter is on mark but not when on space To conserve the amount ofcode tape required, the" coding transmitter is run at one-tenth thespeed of the message transmitter. To retain the 'dot-by-dot codingfeature above explained, code cams are provided which also reverse thesense of transmission on a dot length basis. Between them, these camsrepeat only every 2450 dot lengths, although individually repeatingabout every 100 dot lengths. The reversing action of these cams issuperimposed on the slower action of the coding transmitter with the netresult of producing a non-repeating code while using one-tenth as muchcoding tape as otherwise required.

The enciphering device must beV drivensynchronously with the messagetransmitter. The decoding device must be driven from a phase-correctedsource, also synchronously with the mes- *Y vals, said means includingval cam-controlledl Y 8 switching device, and means vfor coordinating theeffects of the two said transmitters and said means, thereby to producea random interchange of signs of the mark and space signal elementsissuing from the messagevtape transmitter.

2. The combination according to claim 1 and including means formaintaining synchronism between the operations of said transmitters andsaid pulse producing means.

3. The combination according to claim 1 and including means for sensingcode perforationsin the tape of said message tape transmitter at adot-unit rate per minute which is a multiple of the perforation sensingrate of said enciphering tape transmitter. Y,

4. The combination according to claim 1 and including means for sensingcode perforations in the tape of said message tape transmitter at Vadot-unit rate per minute which is the same as that of saidcam-controlled switching device.

5. In an enciphering and deciphering telegraph system, mechanism forproducing pulses of different signs to represent the code elements ofmessage characters, said code elements having marking and spacingcharacteristics of fixed baud unit length and Vintegral multiplesthereof; an enciphering tape keyer including a perforated tape and meansfor sensing the perforations therein at a baud frequency rate which isan integral fraction of the operational rate of said pulse producingmechanism; cam-operated switching means jointly operable with said keyerfor transposing the signs of said message pulses in a predeterminedrandom mannerymeans for transmitting a train of signal impulsesresultant from .the combined operation of said mechanism,Y

said keyer and said switching means; a receiving station, anddeciphering means automatically fects of an enciphering device, relaymeans re-v sponsive to said signals, deciphering means in-f cluding adeciphering tape, a tape controlled double-throw switch, andcam-operated reversing switchk means jointly operable for duplicatingthe effects of said enciphering device, and responsive means operativeunder joint control of said relay means and said deciphering means forrestoring the intelligence which would have been carried by said markand space indications without interchange. Y

'7. Apparatus according to claim 6 and including an opaque housing forsaid deciphering tape and means for substantially concealing said tapefrom view while causing it to be utilized in the control of saiddouble-throw switch.

8. In a secrecy telegraph system, a sending station, a code transmitteryat said station for sending out mark and space signals, said transmittercomprising a perforated message tape, a

perforated enciphering tape, said tapes being cooperatively associatedwith tape-controlled switching means operable to select a predeterminedpolarity of potential for characterizing eachk mark and space signal,cam-controlled 'switching means for introducing further polare ityreversals into said characterization, a receiving station, and means atsaid receiving station for so transposing the characterization of saidsignals that the intelligence carried by said message tape is restored.

9. An enciphering system for transposing the marking and spacingelements of a telegraphic signal train in a random manner, said systemcomprising a message tape, an enciphering tape, means for reversing thepolarity of the signal impulses, said means being operable under jointcontrol of the two said tapes, cam-controlled means for subjecting saidsignal impulses to further polarity reversals, and means for effectingall polarity reversals in substantially fixed phase relation to theoperation of a transmitting distributor.

10. In combination, for use in the enciphering system of claim 9, a pairof code-cams, a motor for continuously driving said cams, andtransmission gears having such ratios that the phase relation betweensaid cams changes at a relatively slow rate.

1l. In combination, for use in the enciphering system of claim 9, a pairof code-cams, a motor for continuously driving said cams, andtransmission gears having such ratios that the phase relation betweensaid cams changes at a relatively slow rate, said cams having aperipheral formation such that they cause polarity reversals to beproduced by said switching means in synchronism with the signal impulsesderived under control of said message tape.

12. In a deciphering system operative at a receiving station forrestoring the original intelligence of a telegraphic signal train Whichhas been enciphered by the system of claim 9, a signal-responsive relay,a deciphering tape, a second relay responsive to control by perforationsin said deciphering tape, cam-controlled means operative in conjunctionwith said second relay for further transposing the sense of the receivedsignal impulses, and impulse-responsive means operable by said signalimpulses, after successive transpositions by said second relay and bysaid cam-controlled means, for deriving said original intelligence.

13. In a telegraph system the combination of a transmitting stationcomprising message tape keying means, a rst cryptographic tape keyingmeans, a first code-cam controlled keying means and an output relayoperable in response to the coordinated enciphering action of al1 saidkeying means, a signal transmitter under control of said output relay,and a receiving station comprising relay means responsive to incomingsignals derived from said transmitter, a second cryptographic tapekeying means having a deciphering tape Which is a replica of the tapeemployed in said rst ycryptographic tape keying means, a second code-camcontrolled keying means operable in synchronism with said rst code-camcontrolled keying means, and a translating device operable in responseto the coordinated deciphering action of said signal responsive relaymeans in conjunction with all of said receiving station keying means.

RICHARD E. MATHES.

